Endoprosthetic devices, commonly referred to as stents, are generally implanted to reinforce vessel walls. In one type, the stent is implanted via a catheter by mounting the stent in a collapsed form on the catheter. After positioning the stent in a body vessel, the stent is expanded to a larger diameter either by self-expansion or by the use of a balloon catheter or the like and the catheter removed. These stents have generally included cylindrical springs of stainless steel, sleeves of expandable heat sensitive materials, and expandable sleeves formed of linked metal alloy wires arranged in a zig-zag configuration and expandable metal mesh sleeves as shown in U.S. Pat. No. 4,733 665 to Palmaz issued Mar. 29, 1988; U.S. Pat. No. 4,776,337 to Palmaz issued Oct. 11, 1988; U.S. Pat. No. 4,856,516 to Hillstead issued Aug. 15, 1989; U.S. Pat. No. 4,877,030 to Beck et al. issued Oct. 31, 1989; U.S. Pat. No. 5,007,926 to Derbyshire issued Apr. 16, 1991; U.S. Pat. 5,019,090 to Pinchuk issued May 28, 1991; U.S. Pat. No. 5,041,126 to Gianturco issued Aug. 20, 1991; U.S. Pat No. 5,102,417 to Palmaz issued Apr. 7, 1992; U.S. Pat. No. 5,104,404 to Wolff issued Apr. 14, 1992; U.S. Pat. No. 5,122,154 to Rhodes issued Jun. 16, 1992; U.S. Pat. No. 5,133,732 to Wiktor issued Jul. 28, 1992; U.S. Pat. No. 5,135,536 to Hillstead issued Aug. 4, 1992.
Over time, prior art stents may require an additional or secondary dilation to accommodate or effect further changes in the vessel. The elastic recoil associated with stenotic lesions may require a second dilation to prevent restenosis. The above configurations allow for secondary dilation, but only to a maximum based on the stent design.
Further, a major problem with the use of stents in pediatric patients is that the vessel stops growing where the stent is implanted, particularly where a metal mesh sleeve stent is employed. The adherence of the endothelial cellular layer of the vessel to the stent surface tends to prevent further outward circumferential growth of the vessel. Further growth is required in body vessels of pediatric patients. The use of wire stents that have a low surface area and which may allow endothelial growth are not optimal because of the high local stress on the vessel wall caused by the wires.
Of course, one option is to replace the stent on a regular basis, but this would involve repeated surgeries which both increase costs and risks for the patient. The present stents would only be used in a small child in an emergency due to the limitation of these stents.
The prior art discloses stents which are circumferentially expandable such as the Beck et al. '030 patent. The Beck et al. '030 patent discloses an endoprosthesis for vessels in which a "rolled-up" uninflated stent is placed over an uninflated balloon catheter and inserted into the target vessel. Once in position, the catheter is inflated, thereby "unrolling" and dilating the prosthesis to form a tube-like structure. The catheter is then removed. A second possible dilation of the endoprosthesis is not provided. Further, no provision is made for use in pediatric patients requiring circumferential growth of the vessel.
The Palmaz '665 patent also describes a variable expandable intraluminal vascular stent in which the stent is a wire mesh tube. However no provision is made for circumferential growth of the body vessel or any later secondary dilation of the endoprosthesis because it is limited by a maximum diameter based on the stent design.